Synapse development will be studied in cloned cell lines of nerve and muscle. A myoblast cell line has been shown to participate in synapse formation with spinal cord neurons. This system will be characterized as a step in the development of an all clonal system. A collection of new cell lines has been established. These cells have been cloned and characterized and have many of the electrical, pharmacological and biochemical properties of nerve muscle and glia. The C1300 neuroblastoma as well as five new neuronal cell lines will be screened for their ability to form chemical synapses. The trophic interactions involved in innervation will be studied utilizing cloned lines as well as disaggregated spinal cord cells. The C1300 neuroblastoma interacts with a myoblast cell line to produce a localization of acetylcholine receptors on the muscle surface at the point of neurite contact. The mechanism responsible for the localization of receptors is being studied in this clonal cell line system. A program to establish and characterize cell lines from the nervous system will be continued. Methods will be developed to fractionate cells from the spinal cord and to visualize receptors on living cells.